Low-temperature, diagenetic serpentinization of peridotite clasts in lower Miocene marine conglomerates, Torino Hill, NW Italy

Peridotite clasts in a marine Miocene conglomerate from the Torino Hill (NW Italy) are characterised by an isopachous serpentinized external rim (4-12 mm thick) made up of lizardite, surrounding a non-serpentinized peridotite core. This peculiar structure indicates a diagenetic, post-depositional serpentinization of the peridotite clasts. The conglomerate is cemented by a rim of lizardite, followed by Mg-calcite and Ca-dolomite spar. The burial history of the host sedimentary succession indicates that serpentinization and precipitation of lizardite cements probably occurred at very low temperature (max. 50-60 °C). This is the first reported case of diagenetic, very low temperature serpentinization affecting ultramafite clasts in sedimentary successions.